On Sun, Mar 05, 2006 at 02:42:03PM +0100, Peter Juszack wrote:
You said that you never used AC3 before because you do not receive AC3-channels from your cable network. On my Hauppauge FF-card the firmware must do a trick do deliver AC3 on the SPDIF by encapsulating the AC3 pakets in PCM. Some AV-receivers cannot handle that. I believe that Technotrend is the same.
For S/P-DIF the AC3 pakets are encapsluated into non-linear PCM[2]. The problem is that within the S/P-DIF containers[1] for the AC3 data there are some more bits which are used to indicate `AC3 used'. Now the hardware of the DVB-S cards can not set this `AC3 used' bit and if AV receivers test for this bit and ignore the special PCM structure[2] the AC3 data will be handled as linear PCM which is generating nasty noise.
[1] S/P-DIF is part of ISO/IEC 60958 [2] Nonlinear PCM for AC3 over S/P-DIF as described in ISO/IEC 61937
Werner